Effects of Aeration, Alum Treatment, Liming, and Organic Matter Application on Phosphorus Exchange between Soil and Water in Aquaculture Ponds at Auburn, Alabama

Application of readily-oxidizable organic substrate to laboratory soil-water systems and fish ponds caused anaerobic conditions in bottom soil and water, and concentrations of soluble reactive phosphorus (SRP) increased. Aeration of ponds increased total phosphorus (TP) concentrations by suspending soil particles in the water, but SRP concentrations declined because of increased oxy- genation of bottom water and soil, Alum [Al₂(SO₄)₃·14H₂O] treatment of ponds reduced SRP and TP concentrations in ponds, but the low concentration of alum used, 20 mg/L, had little residual effect on phosphorus concentration. Application of agricultural limestone at 0.2 kg/m² to ponds with soil pH of 5.5 and Ca²⁺ concentration of 5 mg/L did not affect SRP and TP concentration. Unless pond soils were anaerobic at their surfaces, a condition not acceptable in thermally-unstratified fish ponds, soils released little phosphorus to the water. Strong adsorption of phosphorus by soils in intensive ponds with feeding is beneficial, because removal of phosphorus by aerobic soils is a control on excessive phytoplankton growth. In fertilized ponds, phosphorus must be applied at frequent intervals to replace phosphorus removed from the water by soils.     

Factors affecting respiration in dry pond bottom soils

The potential influence of drying, liming, tilling, bacterial augmentation, and nitrogen fertilization on respiration of pond bottom soil exposed to air between crops was evaluated in laboratory studies using soil respiration chambers. The optimum soil moisture concentration for respiration was 12–20%, and further drying decreased soil respiration. Soil respiration was greatest at pH 7.5–8.0, and both calcium hydroxide and calcium carbonate were effective in enhancing respiration of acidic soil. Pulverization of soil to eliminate the hard surface crust formed on drying accelerated respiration, thus tilling of pond bottom soils would be expected to increase respiration. Nitrogen fertilization showed some benefit to soil respiration, but there was no value in bacterial augmentation. These laboratory findings provide background information useful to pond studies on bottom soil treatments.     

Evaluation of the Ultraviolet Spectrophotometric Method for the Measurement of Total Nitrogen in Water

Abstract.— A simple, accurate, and environmentally sound procedure based on spectroscopy in the UV range was modified to measure total nitrogen concentrations in both freshwater and brackishwater. Water samples from freshwater fish ponds were analyzed for total nitrogen with the persulfate digestion method followed by analysis of nitrate with the UV method for comparison with the NAS reagent method. Brackishwater samples with salinities of 8 to 10 ppt from shrimp ponds were digested by the persulfate method and analyzed with the UV method. Percentage recovery of nitrogen and also precision were evaluated for the UV method. Nitrate concentrations in the freshwater persulfate digests determined by the UV method were similar to those obtained by the NAS reagent method ( P < 0.05). The slope of the regression line did not differ from 1.0 ( P < 0.05). Precision of both methods was acceptable over the range of nitrogen concentration used, but precision of the UV method tended to be better than that of the NAS method. Spike recovery averaged 97.4% in the NAS reagent method and 107.2% in the UV method. Interference from organic matter was minor in the UV method, because virtually all of the organic matter was oxidized during the digestion. Precision with brackishwater samples was slightly better than the freshwater samples and percentage spike recovery averaged 102.8%. Because spectrophotometers in most laboratories have the capability of reading in the UV range, the UV method is an attractive alternative for total nitrogen analysis.     

Measurement of 5-day biochemical oxygen demand without sample dilution or bacterial and nutrient enhancement

A direct method for measuring the 5-day biochemical oxygen demand (BOD₅) of aquaculture samples that does not require sample dilution or bacterial and nutrient enrichment was evaluated. The regression coefficient (R²) between the direct method and the standard method for the analyses of 32 samples from catfish ponds was 0.996. The slope of the regression line did not differ from 1.0 or the Y-intercept from 0.0 at P = 0.05. Thus, there was almost perfect agreement between the two methods. The control limits (three standard deviations of the mean) for a standard solution containing 15 mg/L each of glutamic acid and glucose were 17.4 and 20.4 mg/L. The precision of the two methods, based on eight replicate analyses of four pond water samples did not differ at P = 0.05.     

Economics of Sustainable Intensification of Aquaculture: Evidence from Shrimp Farms in Vietnam and Thailand

There is growing interest in sustainable intensification of aquaculture production. Yet little economic analysis has been done on farm‐level effects of the economic sustainability of production intensification. Data from 83 shrimp farms (43 in Vietnam and 40 in Thailand) were used to identify (through principal component and cluster analyses) 13 clusters of management practices that reflected various scales of production intensity that ranged from 0–1999 kg/ha/crop to 10,000 kg/ha/crop and above, for both Penaeus monodon and Litopenaeus vannamei in Vietnam and Thailand. The clusters identified reflected sets of management practices that resulted in differing yields despite similarities in stocking densities among some clusters. The enterprise budget analysis developed showed that the more intensively managed clusters outperformed the less intensively managed clusters in economic terms. More intensively managed farm clusters had lower costs per metric ton of shrimp produced and were more profitable. The greater yields of shrimp produced per hectare of land and water resources in more intensively managed shrimp farms spread annual fixed costs across a greater volume of shrimp produced and reduced the cost per metric ton of shrimp. Costs per metric ton of shrimp produced decreased from the lowest to the highest intensity level (from US$10,245 at lowest intensity to US$3484 at highest for P. monodon and from US$24,301 to US$5387 for L. vannamei in Vietnam and from US$8184 at the lowest intensity level to US$3817 at the highest intensity level per metric ton for L. vannamei in Thailand). Costs of pond amendments used in shrimp production were particularly high in Vietnam and largely unwarranted, whereas fixed costs associated with the value of land, production facilities, equipment, and labor were sufficiently high in Thailand so that net returns were negative in the long run. Nevertheless, economic losses in Thailand were less at greater levels of intensification. The study demonstrated a clear value proposition for shrimp farmers to use natural resources (such as land) and other inputs in an efficient manner and supports findings from corresponding research on farm‐level natural resource use efficiency. Additional research that incorporates economic analysis into on‐farm studies of sustainable intensification of aquaculture is needed to provide ongoing guidance related to sustainable management practices for aquaculture.     

A simple method for calculating liming rates for fish ponds

The pH change in 40 ml of buffer caused by 20 g dry soil may be multiplied by 5600 to provide the lime requirement of mud in a fish pond. The buffer contains 10 g p-nitrophenol, 7.5 g boric acid, 37 g potassium chloride, and 5.25 g potassium hydroxide dissolved and diluted to 1000 ml with distilled water; the buffer pH is adjusted to 8.00.     

Chlorination of Channel Catfish Ponds

Abstract— Laboratory studies with pond water samples revealed that 5 mg/L active chlorine was needed to provide enough chlorine residual to reduce biological activity. Treatment of channel catfish ponds with repeated, 0.1-mg/L doses of active chlorine from calcium hypochlorite at 6- to 8-d intervals, as sometimes done by catfish farmers, had little influence on water quality. Dissolved oxygen, total ammonia-nitrogen, and chlorophyll a concentrations and pH were similar between treated and control ponds. Concentrations of chemical oxygen demand and particulate organic matter were seldom different between treated and control ponds. Channel catfish survival and net production were not improved by chlorine treatment. Thus, chlorination of production ponds during the grow-out period is not a useful technique. Treatment of sediment samples from ponds with up to 1,200-mg active chlorinelkg soil did not reduce bacterial abundance, so chlorination of bottoms of empty ponds may not he an effective disinfection procedure. Chlorination of pond waters with 30-mg/L active chlorine caused complete kill of bacteria 24 h after treatment, although heterotrophic bacteria quickly re-populated the water. Thus, chlorination can be an effective way to disinfect ponds before stocking.     

Landscape labelling: A concept for next-generation payment for ecosystem service schemes

Current payment for environmental service (PES) schemes face challenges in the form of evaluation of opportunity costs and ecosystem service delivery, high transaction costs, and difficulties in ensuring conditionality. Even when these conditions are met, PES may be undermined by a lack of inclusivity, leading to societal conflicts over land use. We propose a new PES-type approach that we call Landscape Labelling that seeks to overcome these problems by combining PES and product certification principles applied at a landscape scale with local benefits realized at the community level.     

Effect of organic matter concentration on agricultural limestone dissolution in laboratory soil–water systems

Laboratory soil – water systems in which soil organic matter was increased by 0.0%, 0.5%, 1.0%, 2.0% and 4.0% by adding dry, chopped ryegrass (Lolium perenne) shoots to sandy soil containing 0.06% organic matter. Agricultural limestone was added to the systems, and pH, alkalinity and hardness of the water were monitored for 65 days. The pH, alkalinity and hardness increased with greater soil organic matter concentration. Amounts of carbon dioxide released by microbial respiration increased at the higher soil organic matter concentrations, and this resulted in more rapid and greater solubility of agricultural limestone. The results suggest that greater soil organic matter concentrations in ponds favour the rate and extent of agricultural limestone dissolution.